[jira] [Created] (HDFS-14332) NetworkTopology#getWeightUsingNetworkLocation return unexpected result

["He Xiaoqiao (JIRA)" <ji...@apache.org>]

He Xiaoqiao created HDFS-14332:
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             Summary: NetworkTopology#getWeightUsingNetworkLocation return unexpected result
                 Key: HDFS-14332
                 URL: https://issues.apache.org/jira/browse/HDFS-14332
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: namenode
            Reporter: He Xiaoqiao
            Assignee: He Xiaoqiao


Consider the following scenario:
1. there are 4 slaves and topology like:
Rack: /IDC/RACK1
   hostname1
   hostname2
Rack: /IDC/RACK2
   hostname3
   hostname4
2. Reader from hostname1, and calculate weight between reader and [hostname1, hostname3, hostname4] by #getWeight, and their corresponding values are [0,4,4]
3. Reader from client which is not in the topology, and in the same IDC but in none rack of the topology, and calculate weight between reader and [hostname1, hostname3, hostname4] by #getWeightUsingNetworkLocation, and their corresponding values are [2,2,2]
4. Other different Reader can get the similar results.
The weight result for case #3 is obviously not the expected value, the truth is [4,4,4]. this issue may cause reader not really following arrange: local -> local rack -> remote rack. 

After dig the detailed implement, the root cause is #getWeightUsingNetworkLocation only calculate distance between Racks rather than hosts.

I think we should add constant 2 to correct the weight of #getWeightUsingNetworkLocation.



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